Unbalanced of_node_put{get} on initial 'from' node?

Unbalanced of_node_put{get} on initial 'from' node?

[Shawn Guo]

Hi Grant,

I'm running into some problem when using of_find_matching_node().
Here is the pseudo code.

void foo(struct platform_device *pdev)
{
	struct device_node *from = pdev->dev.parent->of_node;
	struct device_node *np;

	np = of_find_matching_node(from, matches); /* matches is a global of_match */
	while (np) {
		...... /* do stuff with the node */
		np = of_find_matching_node(np, matches);
	}
}

I found with above function executed that the node 'from'
gets an unbalanced 'of_node_put' call in of_find_matching_node().  Was
of_find_matching_node() designed in this way?  Or should it get
of_node_put{get} on 'from' node balanced?

Using helper macro for_each_matching_node does not run into this
problem, because the initial 'from' node is NULL, which will get
bypassed by of_node_put.

-- 
Regards,
Shawn

Re: Unbalanced of_node_put{get} on initial 'from' node?

[Grant Likely]

On Fri, Jul 15, 2011 at 12:39:58AM +0800, Shawn Guo wrote:
> Hi Grant,
> 
> I'm running into some problem when using of_find_matching_node().
> Here is the pseudo code.
> 
> void foo(struct platform_device *pdev)
> {
> 	struct device_node *from = pdev->dev.parent->of_node;
> 	struct device_node *np;
> 
> 	np = of_find_matching_node(from, matches); /* matches is a global of_match */
> 	while (np) {
> 		...... /* do stuff with the node */
> 		np = of_find_matching_node(np, matches);
> 	}
> }
> 
> I found with above function executed that the node 'from'
> gets an unbalanced 'of_node_put' call in of_find_matching_node().  Was
> of_find_matching_node() designed in this way?  Or should it get
> of_node_put{get} on 'from' node balanced?

Yes it is.  The node returned from of_find_matching node has already
had "of_node_get()" called on it, and the caller is expected to
release it.  So, any node passed into of_find_matching_node() instead
of NULL as the starting point must have already had of_node_get()
called on it.

g.